A polarizing plate has been generally used as a structure where a protection film is laminated on one surface or both surfaces of a polarizer formed of a polyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin dyed with a dichromatic dye or iodine by using an adhesive. In the related art, a triacetyl cellulose (TAC)-based film has been mainly used as the protection film for the polarizing plate, but there is a problem in that in the case of the TAC film, since moisture permeability is high, the TAC film is easily deformed under the high temperature and high humidity environment. Accordingly, recently, protection films of various materials which can replace the TAC film have been developed, and for example, a method where polyethylene terephthalate (PET), cycloolefin polymer (COP), and acryl-based films, and the like are used alone or are used while being mixed is proposed.
Among them, since the polyethylene terephthalate film has lower costs and excellent durability as compared to the other polymer films, in order to reduce manufacturing costs of the polarizing plate, attempts for using the polyethylene terephthalate film as the protection film for the polarizer have continued. However, there is a problem in that in the case of the polyethylene terephthalate film, since adhesion force with a polyvinyl alcohol-based adhesive used for adhesion of the polarizer and the protection film in the related art is low, after the polarizing plate is manufactured, stripping and lifting of the protection film and the like easily occur to degrade an optical property and durability of the polarizing plate.
Further, there is a problem in that since the polyethylene terephthalate film has a refractive index and a retardation value that are higher than those of the other polymer film, in the case where the polyethylene terephthalate film is applied as the protection film, optical inferiority, such as a reduction in transmittance of the polarizing plate due to an increase in reflectance or the occurrence of a rainbow phenomenon due to an interference effect, occurs.
Therefore, there is a demand for a technology of developing a polarizing plate having excellent durability to not easily cause deformation even under a high temperature and high humidity environment and having an excellent optical property even though a polyethylene terephthalate film is used as a protection film.